•    Due to weathering of rocks different kinds of sand particles are formed like sand, clay etc., their ratio in soil depends on the kind of rock from which these particles are formed. 
•    soil contain various biotic and abiotic factors. Former includes bacteria, plant roots, earthworms, nematodes etc. Later includes water, air, minerals etc. 
•    Classification of soil is based on proportion of soil particles of various sizes. 
    (a) Sandy Soil: Soil contains greater proportion of big size particles. 
    (b) Clayey Soil: Proportion of fine particles is relatively higher 
    (c) Loamy Soil: Amount of large and fine particles is almost same. 
•   On the basis of size, soil particles are broadly classified into following categories:
    (i) Gravel or Stones → 2 mm
    (ii) Sand 0.05 to 2 mm
    (iii) Silt and clay below 0.05 mm

•   Properties of different soil depends on sizes of soil particles it have. In sandy soil, particles size is quite large so they can not fit closely together and have large spaces between them. These spaces are filled with air. Thus, soil is well  aerated having less             water holding capacity. Hence sandy soil is light, well aerated and dry. 
•    In clayey soil, soil particles are much smaller, tightly packed and having little air space. Thus, clayey soil, have little air, more water holding capacity and great amount of humus. 
•    Loamy is best soil for growing plants. Loamy soil contains equal mixture of sand, silt and clay soil particles. Size of silt particles is between sand and clay. Loamy soil have great water holding capacity, large amount of humus and is well aerated so, it is              regarded as best soil for growth of plants.